Alcohol Chemistry and You

Ethyl alcohol (ethanol, CH₃CH₂OH) is a low molecular weight aliphatic (open chain) compound, which is completely miscible with water. This characteristic is due to its hydroxyl (-OH) group, which forms intermolecular hydrogen bonds to water. Thus, the hydroxyl group is referred to as being hydrophilic (water-attracting), whereas the ethyl (C₂H₅-) group is referred to as being hydrophobic (water-repelling).

Because of the complete miscibility with water, ethyl alcohol is readily distributed throughout the body in the aqueous blood stream after consumption. Also and because of this water solubility, it is readily crosses important biological membranes, such as the blood brain barrier, to affect a large number of organs and biological processes in the body.

The passage of ethyl alcohol across biological membranes occurs by a process of simple passive diffusion along concentration gradients, in accordance with Fick’s law.

Fick's Law: Describes passive movement molecules down its concentration gradient.

* for lipid diffusion, lipid: aqueous partition coefficient -- major determinant of drug mobility

* partition coefficient reflects how easily the drug enters the lipid phase from the aqueous medium.

(Taken From: Katzung, B. G. Basic Principles-Introduction , in Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, p 5.)

Absorption of ethyl alcohol into the blood can occur through the skin and via the lungs, though the major route of taking ethyl alcohol into the body is by drinking alcoholic beverages.

Absorption through the skin has been confirmed by a report (Dalt et al, 1991) of a case of a 1 – month old infant who became intoxicated as a result of absorption of ethyl alcohol from dressings applied to the stump of the umbilical cord and the skin adjacent to it.

Additional confirmation of skin absorption comes from a microdialysis study in which a long probe with was inserted under the skin for a distance of 3 cm. Ethyl alcohol was then placed in a small area on the skin above the probe while the subcutaneous area was being perfused. Analysis of the perfusate indicated the presence in an amount that was related to the extent of skin exposure (Anderson et al, 1991).

Inhalation of ethyl alcohol vapor allows the absorption of ethyl alcohol across the pulmonary epithelium. This method of ethyl alcohol administration has formed the basis of a simple and effective means of administering alcohol to animals in experimental situations (e. g. Goldstein and Pal, 1971; Becker et al. ).

The advantage of this procedure is the ability to maintain ethyl alcohol exposure to a consistent amount of ethyl alcohol for a determined amount of time. This produces stable concentrations of ethyl alcohol in the animal in contrast to fluctuating levels seen after other routes of administration (see below). An extreme illustration of absorption via the inhalation route is the case of an infant who died when isopropanol was added to the humidifier of a mechanical ventilator by mistake. The child was initially found profoundly intoxicated (Vicas and Beck, 1993).

Drinking is the primary means by which ethyl alcohol is taken into the human body.

Ethyl alcohol taken in via ingestion passes from the mouth down the esophagus and into the stomach and on into the small intestine. At each point along the way ethyl alcohol can be absorbed into the blood stream. However, the majority of the ethyl alcohol is absorbed from the stomach (approx. 20%) and the small intestine (approx. 80%). In general drinking more alcohol within a certain period of time will result in increased blood alcohol concentrations (BAC) due to more ethyl alcohol being available to be absorbed into the blood. However, it should be noted that there are a number of factors that can influence ethyl alcohol absorption from the gastrointestinal tract. Therefore, the previous statement is true only if other factors such as the rate of gastric emptying, the presence of food, the concentration of the ethyl alcohol taken in, the type of alcohol containing beverage consumed, and other factors such as gastrointestinal motility and blood flow remain constant.

Gastric emptying seems to be the most important determinant of the rate of absorption of ethyl alcohol taken in orally. In general the faster the gastric emptying, the more rapid absorption. Therefore, factors, which influence gastric emptying, influence absorption. One of the most important factors is the presence of food. Food delays gastric emptying and therefore delays absorption of ethyl alcohol . Interestingly, the type of food, whether fat, carbohydrate, or protein, does not seem to be a factor in the absorption of ethyl alcohol. Physiological factors such as strenuous physical exercise also delay gastric emptying, thus decrease ethyl alcohol absorption. Additional factors such as drugs (e.g. nicotine, marijuana, and ginseng), that modify physiological factors regulating gastric emptying also modify ethyl alcohol absorption in a predicted manner.

The ethyl alcohol concentration of the beverage appears to be an important factor in absorption from the gastrointestinal tract. If just Fick’s Law were in effect then it would be expected that the higher the concentration of ethyl alcohol consumed the move rapid the absorption, however it appears that higher concentrations of alcohol may actually delay absorption. Though the precise reason for this finding is not known, it can be speculated that higher concentrations of ethyl alcohol may diminish the movement of the alcohol from the stomach through the pylorus (opening from stomach to small intestine) and into the small intestine.